The evidence for this conclusion is provided by the immunohistochemical patterns of the DNA damage signalling marker γH2AX, as well as activated forms of the ATM, ATR, Chk1 and Chk2 kinases on the sections of all medulloblastomas in our cohort, contrary to the absence of these DDR markers on sections of normal cerebellum. The gene discussed is CHEK1; the disease is medulloblastoma.